Method and System for Combining DFT-Transformed OFDM and Non-Transformed OFDM

ABSTRACT

Methods and systems are provided that enable an OFDM transmitter to be used for transmitting conventional OFDM or a form of transformed OFDM. A technique is provided for transforming a coded and modulated sequence of samples prior to an IFFT that enables the transformed sequence of samples to be transmitted using conventional OFDM or transformed OFDM. The selection of a transform function for transforming the coded and modulated sequence of samples may be based on optimizing the transform function for particular operating conditions between the transmitter and receiver. In some embodiments of the invention OFDM and time transformed OFDM are multiplexed in time and/or frequency in a transmission frame. In some embodiments of the invention a pilot pattern is provided in which the pilot are sent using OFDM and data is sent using OFDM and/or transformed OFDM.

PRIORITY CLAIM INFORMATION

This application is a continuation of U.S. patent application Ser. No.16/273,302 filed Feb. 12, 2019, titled “Method and System for CombiningDFT-Transformed OFDM and Non-Transformed OFDM”, by Jianglei Ma, WenTong, Ming Jia, Hua Xu, Peiying Zhu, Hang Zhang which is a continuationof

U.S. patent application Ser. No. 15/790,678, filed Oct. 23, 2017, titled“Method and System for Combining DFT-Transformed OFDM andNon-Transformed OFDM”, by Jianglei Ma, Wen Tong, Ming Jia, Hua Xu,Peiying Zhu, Hang Zhang (issued as U.S. Pat. No. 10,237,206 on Mar. 19,2019), which is a continuation of

U.S. patent application Ser. No. 15/195,083, filed Jun. 28, 2016, titled“Method and System for Combining DFT-Transformed OFDM andNon-Transformed OFDM”, by Jianglei Ma, Wen Tong, Ming Jia, Hua Xu,Peiying Zhu, Hang Zhang, (issued as U.S. Pat. No. 9,973,365 on May 15,2018), which is a continuation of

U.S. patent application Ser. No. 14/251,629, filed Apr. 13, 2014, titled“Method and System for Combining OFDM and Transformed OFDM”, (issued asU.S. Pat. No. 9,407,487 on Aug. 2, 2016), which is divisional of

U.S. patent application Ser. No. 13/047,259, filed Mar. 14, 2011, titled“Method and System for Combining OFDM and Transformed OFDM” (issued asU.S. Pat. No. 8,773,974 on Jul. 8, 2014), which is a divisional of

U.S. patent application Ser. No. 11/909,567, filed Sep. 24, 2007 (issuedas U.S. Pat. No. 7,929,407 on Apr. 19, 2011), titled “Method and Systemfor Combining OFDM and Transformed OFDM”, which is a U.S. National Stageapplication of

International Application No. PCT/CA2006/000464, filed Mar. 30, 2006,titled “Method and System for Combining OFDM and Transformed OFDM”,which claims the benefit of priority to:

U.S. Provisional Application No. 60/674,878, filed Apr. 26, 2005, titled“MIMO-OFDM Air Interface”, and

U.S. Provisional Application No. 60/666,548, filed Mar. 30, 2005, titled“MIMO-OFDM Air Interface”.

All of the above identified Applications are incorporated by referencein their entireties as though fully and completely set forth herein.

The claims in the instant application are different than those of theparent application or other related applications. The Applicanttherefore rescinds any disclaimer of claim scope made in the parentapplication or any predecessor application in relation to the instantapplication. The Examiner is therefore advised that any such previousdisclaimer and the cited references that it was made to avoid, may needto be revisited. Further, any disclaimer made in the instant applicationshould not be read into or against the parent application or otherrelated applications.”

FIELD OF THE INVENTION

The invention relates to the field of wireless communications, morespecifically to systems and methods employing orthogonal frequencydivision multiplexed (OFDM) transmission.

BACKGROUND OF THE INVENTION

Orthogonal frequency division multiplexing (OFDM) is a particular formof frequency division multiplexing that distributes data over a numberof carriers that have a very precise spacing in the frequency domain.The precise spacing and partially overlapping spectra of the carriersprovides several benefits such as high spectral efficiency, resiliencyto radio frequency interference and lower multi-path distortion. Due toits beneficial properties and superior performance in multi-path fadingwireless channels, OFDM has been identified as a useful technique in thearea of high data-rate wireless communication, for example wirelessmetropolitan area networks (MAN). Wireless MAN are networks to beimplemented over an air interface for fixed, portable, and mobilebroadband access systems.

In another type of frequency division multiplexing, rather than usingclosely spaced frequencies of OFDM, the spectra of adjacent channels aremore or less distinct, and bandpass filtering is typically employed toseparate channels. This will be referred to as “conventional frequencydivision multiplexing”.

Orthogonal frequency division multiplexing is beneficial in thatmultiple input multiple output (MIMO) and collaborative MIMOtransmission schemes are easily implemented thereon. Furthermore, theuse of orthogonal frequency division multiplexing allows for flexibleand efficient pilot designs. Also, problems related to noise enhancementcan be avoided during signal processing at the receiver.

The use of conventional frequency division multiplexing has a lower Peakto Average Power Ratio (PAPR). A disadvantage is that it causes noiseenhancement.

SUMMARY OF THE INVENTION

According to one broad aspect, the invention provides a methodcomprising, within an available spectral resource: transmitting withOFDM multiplexing on selected sub-carriers and selected OFDMtransmission durations; transmitting with T-OFDM (transformed OFDM)multiplexing or direct multiple sub-carrier multiplexing on selectedsub-carriers and selected OFDM transmission durations that do notoverlap with OFDM transmissions.

In some embodiments, transmitting with OFDM multiplexing andtransmitting with T-OFDM multiplexing comprises: transmitting arespective signal from each of a plurality of antennas, each signalcomprising OFDM multiplexing or T-OFDM multiplexing. In someembodiments, transmitting a respective signal from each of a pluralityof antennas, each signal comprising OFDM multiplexing or T-OFDMmultiplexing comprises using a distinct frequency resource for eachtransmitter.

In some embodiments, transmitting a respective signal from each of aplurality of antennas comprises transmitting from a plurality oftransmitters.

In some embodiments, transmitting a respective signal from each of aplurality of antennas comprises transmitting from a single transmitter.

In some embodiments, transmitting a respective signal from each of aplurality of antennas, each signal comprising OFDM multiplexing orT-OFDM multiplexing comprises transmitting a respective signal from eachof a plurality of transmit antennas using common frequency resources forat least two antennas such that MIMO processing will be required toseparate the signals upon receipt.

In some embodiments, transmitting a respective signal from each of aplurality of antennas comprises transmitting from a single transmitter.

In some embodiments, transmitting a respective signal from each of aplurality of antennas comprises transmitting from a plurality oftransmitters so as to implement a virtual MIMO transmission.

In some embodiments, the method as summarized above further comprises:mapping symbols to the selected sub-carriers for OFDM multiplexing usinga sub-band mapping or a diversity mapping; transforming symbols to betransmitted with T-OFDM to produce transformed symbols and mapping thetransformed symbols to the selected sub-carriers for T-OFDM using asub-band mapping or a diversity mapping.

In some embodiments, transmitting from a single transmitter comprises:transmitting with OFDM multiplexing during selected OFDM transmissiondurations; transmitting T-OFDM multiplexing during OFDM transmissiondurations distinct from the OFDM transmissions used for OFDMmultiplexing.

In some embodiments, transmitting with OFDM multiplexing and T-OFDMmultiplexing comprises: for each of at least one frequency resourceallocation consisting of a plurality of subcarrier frequencies:selecting transmitting using OFDM multiplexing and transmitting usingT-OFDM multiplexing.

In some embodiments, the at least one frequency resource allocationcomprises a plurality of resource allocations each consisting of arespective contiguous set of sub-carriers or a distributed set ofsub-carriers.

In some embodiments, for each of at least one frequency resourceallocation consisting of a plurality of sub-carrier frequenciesselecting transmitting using OFDM multiplexing and transmitting usingT-OFDM multiplexing comprises: multiplying a respective set of symbolsby a selected one of two different transform matrices that result inOFDM multiplexing and T-OFDM multiplexing respectively.

In some embodiments, T-OFDM multiplexing comprises multiplying an inputset of symbols by an FFT matrix prior to IFFT processing.

In some embodiments, the method further comprises transmitting pilots.

In some embodiments, the method further comprises transmitting pilotsfrom each antenna on sub-carriers selected from sub-carriers beingutilized by that antenna.

According to another broad aspect, the invention provides a multiplexingmethod comprising: selecting one of at least two transform functions tobe a selected transform function; performing the selected transform on aset of input symbols to produce a transformed sequence of samples;performing an inverse fast Fourier transform (IFFT) of the transformedsequence of samples to produce a multiplexer output.

In some embodiments, the two transform functions consist of an identitymatrix and a non-identity matrix.

In some embodiments, the non-identity matrix is an FFT matrix, fastHadamard transform, or a wavelet transform.

In some embodiments, a transmitter is adapted to implement the method assummarized above.

In some embodiments, a plurality of transmitters is adapted tocollectively implement the method as summarized above.

In some embodiments, a transmitter is adapted to implement the method assummarized above.

According to another broad aspect, the invention provides a methodcomprising, within an available spectral resource: adaptively switchingbetween transmitting to a receiver with OFDM multiplexing andtransmitting to the receiver with T-OFDM or direct multiple carriermultiplexing.

In some embodiments, adaptively switching between transmitting to areceiver with OFDM multiplexing and transmitting to the receiver withT-OFDM or direct multiple carrier multiplexing comprises: at atransmitter processing each set of symbols by one of two transformfunctions one of which results in OFDM multiplexing, the other of whichresults in T-OFDM multiplexing.

In some embodiments, the method further comprises receiving feedback toselect which of the two transform functions to use.

In some embodiments, the method further comprises selecting between thetwo transform functions on the basis of one or more of SNR, traffictype, head room in a power amplifier.

In some embodiments, a transmitter is adapted to implement the method assummarized above.

In some embodiments, the transmitter comprises: a transformer adapted toapply a selected one of the two transform functions to a set of inputsymbols; an IFFT that receives an output of the transform function.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theattached drawings in which:

FIG. 1 contains various block diagrams for implementing a firstconstituent multiplexing method that is equivalent to conventional OFDM;

FIG. 2 contains various block diagrams for implementing a secondconstituent multiplexing method, transformed OFDM;

FIG. 3 contains various block diagrams for implementing a thirdconstituent multiplexing method, direct multiple sub-carriermultiplexing;

FIG. 4 is a block diagram of a first example of the co-existence of OFDMand transformed OFDM in transmissions from multiple transmitters;

FIG. 5 is a block diagram of a second example of the co-existence ofOFDM and transformed OFDM in transmissions a single transmitter;

FIG. 6 is a block diagram of a third example of the co-existence of OFDMand transformed OFDM in MIMO transmissions of a single multipletransmitter;

FIG. 7 is a block diagram of a fourth example of the co-existence ofOFDM and transformed OFDM in MIMO transmissions of multipletransmitters;

FIGS. 8 and 9 are block diagrams of OFDM transmitters according toembodiments of the invention;

FIG. 10 is a schematic diagram of a transmission frame according to anembodiment of the invention;

FIG. 11 is a schematic diagram of a transmission frame according toanother embodiment of the invention;

FIG. 12 is a schematic diagram of a transmission frame according to afurther embodiment of the invention;

FIG. 13 is a schematic diagram of a pilot pattern for FDM according toan embodiment of the invention; and

FIG. 14 is a block diagram of an OFDM transmitter according toembodiment of the invention.

FIG. 15 is a block diagram of a cellular communication system;

FIG. 16 is a block diagram of an example base station that might be usedto implement some embodiments of the present invention;

FIG. 17 is a block diagram of an example wireless terminal that might beused to implement some embodiments of the present invention;

FIG. 18 is a block diagram of a logical breakdown of an example OFDMtransmitter architecture that might be used to implement someembodiments of the present invention; and

FIG. 19 is a block diagram of a logical breakdown of an example OFDMreceiver architecture that might be used to implement some embodimentsof the present invention.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

In OFDM a wideband signal is transmitted on multiple independentparallel narrowband orthogonal carriers. A multicarrier transmitter suchas an OFDM transmitter can have a high Peak-to-Average-Power Ratio(PAPR). The OFDM transmitter has a high power amplifier suitable to meetpeak power requirements. IFFT (inverse fast Fourier transform) has alsobeen applied to realize orthogonal multiplexing of multipletransmitters.

In conventional FDM (frequency division multiplexing) there is no IFFTprocessing of a signal before transmission and transmission occurs on asingle carrier or multiple separated carriers. In addition, modulationschemes used for single carrier transmitters, such as QAM and QPSK havea smaller dynamic range so the PAPR is smaller than for the OFDMtransmitter having a similar transmission range.

An advantage of an OFDM transmitter over a conventional FDM transmitteris a higher spectral efficiency. A disadvantage of an OFDM transmitteras compared to a conventional FDM transmitter is a higher PAPR resultingin a power amplifier in the OFDM transmitter that has a higher cost.OFDM also allows for advanced MIMO applications, flexible and convenientpilot arrangements, and flexible and efficient sub-channelization.

An advantage of a conventional FDM transmitter over an OFDM transmitteris that due to a less noisy output coverage within the cell is better.

When a transmitter is a great distance from a receiver it may bedesirable to modify the transmitted signal to improve a signal to noiseratio and reduce a possibility of errors at a receiver end. Conversely,when the transmitter and receiver are in close proximity it may bedesirable to modify the transmitted signal to employ a high spectralefficiency.

In some embodiments, methods and systems are provided in which a signalprocessing step is added to the technique for processing the signal inthe OFDM transmitter to enable the signal to be modified beforetransmission to meet different operating conditions. In someembodiments, a transmitter is equipped to produce a signal that isselectively modified to result in a conventional OFDM signal or in theform of a conventional FDM signal.

In some embodiments, the processing step is a transformation implementedusing a transformation function. Depending on the selection of thetransformation function for a given implementation, the transformationmay produce an output that has transmission characteristics bounded bythe transmission characteristics of OFDM and conventional FDM. In someimplementations, the processing step may be performed in conjunctionwith a frequency domain decision feedback equalizer (DFE).

In some embodiments, the transmitter is a mobile terminal while in otherembodiments, the transmitter is a base station. The transformation maybe particularly useful in a mobile terminal as reducing the PAPR has aneffect of reducing an amount of power amplification needed fortransmitting a signal. Reducing power amplification may lower energyconsumption and lower energy consumption results in a longer batterylife for battery powered transmitters.

Embodiments of the invention provide various mechanisms for combiningvarious constituent multiplexing structures consisting of OFDM,transformed OFDM, and direct multiple subcarrier modulation, either by asingle transmitter or multiple transmitters.

To begin, three constituent multiplexing structures will be describedwith reference to FIGS. 1, 2 and 3. FIG. 1 shows a block diagram of amultiplexing structure for generating conventional OFDM channels,generally indicated at 200. Input symbols 201 are fed to a mappingfunction 202 the output of which is connected to an IFFT 204. Thepurpose of the mapping function is to map the symbols 201 to particularinputs of the IFFT 204. It is noted that many components might proceedor follow the component shown in FIG. 1, such as coding and modulation,interleaving, or RF up conversion, etc.

Generally indicated at 210 is another multiplexing structure thatproduces the same output as that of structure 210, namely a conventionalOFDM signal output. This includes an additional component 206 which is atransform that performs a transformation on the input symbols 201 beforethe mapping function 202. However, for an OFDM channel, the transformfunction is simply equal to an identity matrix, and as such the outputof the structure of 210 will be indistinguishable from the output of thestructure 200.

A specific example of the mapping function is shown in the structuregenerally indicated at 212. Here the mapping function is a sub-bandmapping 214 that maps the symbols to a contiguous set of sub-carrierfrequencies of the IFFT 204.

Generally indicated at 216 is another example of how the mapping mightbe performed. In this case, the symbols 201 are input to diversitymapping function 218 which maps the symbols to sub-carriers that aredistributed across the sub-carrier frequencies being processed in theIFFT 204.

A second constituent multiplexing structure produces a transformed OFDMsignal. Referring now to FIG. 2, generally indicated at 219 is a blockdiagram of a transmitter that generates a transformed OFDM signal. Inthis case, symbols 201 are input to a transform function 220 the outputof which is fed to mapping function 222 the output of which is input tothe IFFT 204. The transform 220 performs a transformation on the inputsymbols 201. The transformation is not simply the identity matrix as wasthe case in structure 210 of FIG. 1. Specific examples of the transformfunction include a fast Fourier transform (implemented in any suitablefashion, for example a DFT), a wavelet transform (such as a Harr wavelettransform) or a fast Hadamard transform (FHT). In some implementationsthe transform function is represented by an invertible matrix. In someimplementations the transform function is represented by an orthonormalmatrix.

The function of the mapping function 222 and the IFFT 204 is the same asin previous examples. The mapping function 222 maps the outputs of thetransform 220 to selected sub-carriers of the IFFT 204.

A first example of the mapping is generally indicated at 221 where theoutput of the transform 220 is input to a sub-band mapping 224, theresult of which is that a contiguous block of sub-carriers of the IFFT204 are used.

Another example of mapping is shown generally indicated at 223. In thiscase, the output of the transform 220 is input to a diversity mappingfunction 226 which maps the transformed output to a set of sub-carriersthat are distributed throughout the OFDM band of the IFFT 204.

It is readily apparent how the channel structure of FIG. 1 and thechannel structure of FIG. 2 can be implemented using the same physicalimplementation. In particular, the structure 210 in FIG. 1 and thestructure 219 in FIG. 2 are identical with the exception of the factthat a different transform is employed. As such, by dynamicallyselecting the contents of the transform 220, a channel that is an OFDMchannel can be implemented, or a transformed OFDM channel can beimplemented. In some embodiments, transmitters are equipped with such astructure to enable them to dynamically select between operating toproduce OFDM channels or transformed OFDM channels.

Referring now to FIG. 3, shown a third constituent channel type thatwill be referred to as “direct multiple subcarrier multiplexing”,generally indicated at 229. In this case, input symbols 201 are input toa direct multiple sub-carrier modulator 230 to produce an output. Themodulation is direct in the sense that no IFFT or FFT technology isemployed, but rather input symbols are multiplied to particularsub-carriers directly. It is referred to as “multiple” sub-carriermodulation because each input symbol is represented in multiple, in somecases all, of the sub-carriers output by the modulator.

A very specific example is shown generally indicated at 231. In thiscase, the direct multiple sub-carrier modulator consists of a symbolrepeater 232 and a complex spreader 234 that multiplies each repeatedsymbol by a set of complex frequencies to produce an output. It is notedthat the output of the direct multiple sub-carrier multiplexingstructure 231 is in some instances mathematically equivalent to theoutput of the structure 223 of FIG. 2. In particular, when the transform220 is an FFT (or equivalent) and the diversity mapping 226 maps theoutput of the transform 220 to a set of sub-carrier locations that areequally spaced, the output is the same as the output of the structure231 of FIG. 3 where the complex spreader multiplies the repeated symbolsby individual sub-carrier frequencies that are the same as the spacedsub-carrier inputs to the IFFT 204 of FIG. 2. A common feature betweenthe schemes of FIGS. 2 and 3 is that each input symbol 201 ends up beingrepresented on multiple sub-carrier frequencies; in contrast, theconventional OFDM structure of FIG. 1 has each symbol 201 appearing on asingle sub-carrier.

Having defined the three constituent multiplexing structures, variousmechanisms for their co-existence are provided. All such mechanismsinvolve the co-existence of OFDM and one or more of the othermultiplexing approaches, be it transformed OFDM or direct multiplesub-carrier multiplexing. In a particular embodiment, OFDM andtransformed OFDM are supported.

A first example is illustrated in FIG. 4. In this example there is a setof transmitters 240, 242, 244 (only three shown) each of which might forexample be a separate mobile station. Each transmitter is equipped witha respective frequency division multiplexer 246, 248, 250 thatimplements one or more of the three constituent multiplexer structuresof FIGS. 1, 2 and 3. Each transmitter has a respective antenna 252, 254,256. With the embodiment of FIG. 4, the frequency division multiplexers246, 248, 250 each operates using a respective distinct frequencyresource or set of sub-carriers. Given an available set of subcarriers,each transmitter is assigned a different subset of subcarriers andhaving been assigned that set of sub-carriers, one of the threemultiplexer structures are described above is implemented. By separatingout the sub-carriers in this manner, the different channel structurescan co-exist simultaneously.

Another example of the co-existence of these channels will now bedescribed with reference to FIG. 5. Shown is a single transmitter 260having multiple frequency division multiplexers 262, 264, 266 connectedto a single antenna 268. Each frequency division multiplexer 262, 264,266 implements one of the three constituent multiplexer structures ofFIGS. 1, 2 and 3. In this case, the frequency resource is again dividedbetween the different frequency division multiplexers 262, 264, 266 in amanner similar to the distinct transmitters of FIG. 4. Since they areimplemented in a single transmitter, if multiple frequency divisionmultiplexers employ IFFT functionality, a single IFFT could beimplemented for these in combination. Similarly, mapping could beperformed with a single mapper.

Referring now to FIG. 6, shown is another example of how the differentchannel structures can be combined. With the example of FIG. 6, atransmitter generally indicated at 270 has frequency divisionmultiplexers 272, 274, and output antennas 276, 278. Each frequencydivision multiplexer 272, 274 implements one of the three constituentmultiplexer structures of FIGS. 1, 2 and 3. In this case, the twofrequency division multiplexers 272, 274 are not assigned distinctfrequency resources as was the case for the example of FIG. 4. Rather,they are assigned a common frequency resource, and MIMO (multiple input,multiple output) processing is performed at the receiver to separatethese. With the example of FIG. 6, the approach generalizes to anarbitrary number of transmit antennas for a given MIMO channel.Furthermore, the details are only shown for a single frequencyallocation. The structure 270 can be repeated for multiple differenttransmitters as in the FIG. 4 embodiment, or within a single transmitteras in the FIG. 5 embodiment.

In yet another implementation, generally indicated at FIG. 7, astructure similar to that of FIG. 6 is employed, but in which thefrequency division multiplexers 272, 274 are implemented on separatetransmitters 280, 282 respectively. In this case, the frequencyresources again are common and as such this is referred to as “virtualMIMO”, also referred to as collaborative or co-operative MIMO. Areceiver of signals transmitted by the transmitters 280, 282 would useMIMO technologies to separate the two transmissions. The structure ofFIG. 7 can be repeated for multiple different frequency resourceallocations.

With any of the above-described embodiments, the transmitter may operatein an open loop mode in which case there is no feedback input. In otherembodiments the transmitter operates in a closed loop mode, for example,a receiver that receives the transmitted signal sends feedback to thetransmitter to aid in selecting between the various supported FDMvariants, for example by selecting an appropriate transform function.

In some embodiments, the receiver transmits a signal that enables thetransmitter to determine a distance between the transmitter and receiveror to determine an SNR and an available power margin. The receiver maytransmit information that would enable the transmitter to determine abit error rate (BER), a signal to noise ratio (SNR) or a channel qualityestimate. The transmitter may be able to determine whether there is anypower head room to increase power for a given user if signal qualityneeds to be improved. If there is no such room, then an option is toswitch to T-OFDM to reduce PAPR so that power can be increased. Based onthese determinations the transmitter may select a transform function tomodify a coded and modulated signal to improve coverage within the cellby transmitting the transformed signal as transformed OFDM. Conversely,when the transmitter determines from information provided by thereceiver that operating conditions are favorable, for example closeproximity of the transmitter and receiver or favorable transmissionparameters, i.e. BER, SNR the transmitter may select a transformfunction to modify the transmitted signal to employ a high spectralefficiency capacity by transmitting the transformed signal as OFDM.

In some embodiments, the transform function is an FFT. The transformfunction in the form of an FFT may be more efficiently computed using aDFT (discrete Fourier transform) when the number of samples is a powerof 2, but more generally, any approach to computing the FFT can beemployed. The size of the DFT depends on the bandwidth assigned for agiven user. The DFT approach will be assumed in the following specificexample. When the DFT is performed on a single data point (essentiallyan impulse in the time domain), the result is substantially the same asconventional OFDM, which is distributed over all sub-carriers in thetransmission band. When multiple coded and modulated signals are eachtransformed using a DFT smaller than the size of the IFFT the outputs ofthe respective DFTs can be mapped to locations in the IFFT input so asto be processed by the IFFT simultaneously for multi-user signalmultiplexing.

An example of a transform function that includes a DFT is shown below inwhich the DFT is a two sample point DFT represented by the 2×2 matrix[M] within transform function T. The remainder of the elements in theprimary negative sloping diagonal are each equal to one and all otherelements in the matrix equal zero. This type of transform could be usedto transform two symbol sequences simultaneously in a single transmitterwith one sequence being transformed OFDM and the other conventionalOFDM. Alternatively, the transform could be viewed as the sum of twotransformations performed by separate transmitters.

$T = \begin{bmatrix}M_{1,1} & M_{1,2} & 0 & \ldots & 0 \\M_{2,1} & M_{2,2} & 0 & \ddots & \vdots \\0 & 0 & \ddots & \ddots & 0 \\\vdots & \ddots & \ddots & 1 & 0 \\0 & \ldots & 0 & 0 & 1\end{bmatrix}$

After the coded and modulated output is multiplied by such a transform,the transformed output is then input to the IFFT function as before.Different transform functions can be selected for different users.

In some implementations each coded and modulated input is transformedwith a particular transform function. In some implementations the codedand modulated inputs can be collectively transformed by a singletransform function as in the above example matrix. The number of codedand modulated signals is implementation specific depending on a desirednumber of users per transmitter.

In some embodiments, the manner by which the overall bandwidth issubdivided between the different constituent multiplexer types used isupdated dynamically, for example every scheduling period.

In some embodiments of the invention a transform function is aparameterized transform function. The parameterized transform functionmay be for example a parameterized orthonormal matrix, for example aTeoplitz matrix as shown below, where the variables a and b are constantvalues along negative-sloping diagonals.

$T = \begin{bmatrix}1 & a & b & \ldots & 0 \\a & 1 & a & \ddots & \vdots \\b & a & \ddots & \ddots & b \\\vdots & \ddots & \ddots & 1 & a \\0 & \ldots & b & a & 1\end{bmatrix}$

In some embodiments the parameterized transform function is used forpartial response signaling (PRS) in which a controlled amount ofinter-symbol interference (ISI) is permitted. As the amount of ISI isknown, the effect of the ISI can be compensated.

In some embodiments of the invention the transform function is generatedas a function of a desired performance criterion. For a given transformfunction, a function is created, namely Q(T). In some embodiments thefunction Q(T) is used in combination with the transform function tooptimize particular performance criteria, for example minimum meansquare error (MMSE) or minimum bit error rate (BER) at a receiveroutput.

In some embodiments the transform function may be generated by arelation between the transform function T and the function of transformfunction T, Q(T) as min∥TQ(T)−I∥².

In some embodiments the function Q(T) has matrix algebraic formrepresentation. In some embodiments the function Q(T) is a minimizationprocedure, for example a Viterbi trellis search.

In some embodiments, to an embodiment of the invention: T=Q(H), where His the channel matrix. Transform T may be used for channeldecomposition, where (⋅)^(H) represents the Hermitian:

H=UΛV Q(H)=U ^(H)

This can be employed to provide channel pre-equalization andpre-distortion transmission.

In some embodiments, the generation of the transform function mayinclude the generation of a family of transform functions.

In some implementations of the invention the transform function isselected to maximize the receiver output signal to noise ratio. In someimplementations of the invention the transform function is selected tominimize the PAPR. In some embodiments the transmitter selects theparameters of the transform function based on several criteria, such asminimizing the PAPR and/or minimizing the MMSE.

In some embodiments of the invention the receiver may provide feedbackto the transmitter to facilitate the selection of the transformfunction. If the receiver is aware of which transform function is beingused by the transmitter the receiver is able to receive and detect thetransformed sequence of samples when they arrive at the receiver. Insome embodiments of the invention, when the receiver is not involved inselection of the transform function, the transmitter sends anidentification to the receiver of the particular transform function usedin generating the output transmitted by the OFDM transmitter.

In some embodiments the transmitter dynamically and/or adaptivelyoptimizes the transform function for particular operating conditions. Insome embodiments of the invention, there is provided a mechanism thatallows adaptive and dynamic optimization of the transform function tooptimize both transmitter and receiver performance.

In some embodiments of the invention the use of an appropriate transformfunction reduces the PAPR for low power devices.

Various specific examples will now be described with reference to FIGS.8 to 14.

Referring now to FIG. 8 shown is an example of a single input singleoutput (SISO) OFDM transmitter, generally indicated at 600 that isenabled to perform the transform on a sequence of samples in accordancewith an embodiment of the invention. The sequence of samples is providedto coding and modulation logic 610. An output sequence of symbols of thecoding and modulation logic 610 is provided to transform function 620.An output of the transform function 620 is provided to an IFFT function630. The output of the IFFT function 630 is then provided to an antenna640 for transmission.

FIG. 9 shows an example of a multiple input multiple output (MIMO) OFDMtransmitter, generally indicated at 650 that is enabled to perform thetransform in accordance with an embodiment of the invention. In the MIMOOFDM transmitter 650 two portions of a bit stream a single user (notshown) are provided to respective coding and modulation function 660,661. Respective outputs of the coding and modulation functions 660, 661are provided to transform 680. The output of the transform 680 is inputto a space-time coding function 670 that produces a respective outputfor each of two IFFTs 690, 691. The outputs of the IFFTs 690,691 areoutput on antennas 695, 696. With the example of FIG. 9, the transform680 contains a sub-matrix for each of the two inputs from coding andmodulation. If the sub-matrix is an identity matrix, then OFDM is usedfor that input. If the sub-matrix is a non-identity transformation, thentransformed OFDM is used for that input.

The example of FIG. 9 also includes space-time coding function 670 toachieve spatial diversity. Any of the multi-antenna transmitterembodiments may be further supplemented with space-time coding toprovide for spatial diversity.

Except for the transform function 620, 680, the components of the OFDMtransmitters of FIGS. 8 and 9 can be defined in an implementationspecific manner as would be understood by one skilled in the art. In aspecific example, these can be configured to operate in a similar mannerto various components of the transmitter described below with referenceto FIG. 18.

FIG. 9 illustrates a two antenna, single user implementation, but it isto be understood that there may be any number of antennas andcorresponding coding and modulation blocks.

The transform function 620,680 in FIGS. 8 and 9 are each shown to havean additional input indicated by 625 and 685, respectively. In someembodiments these respective inputs are used to provide feedback to thetransform function 620,680 for selection of the transform function in adynamic fashion.

The examples of FIGS. 8 and 9 only implement the constituentmultiplexers of FIGS. 1 and 2 (OFDM and T-OFDM), but not the constituentmultiplexer of FIG. 3 (direct multiple subcarrier modulation). Otherpermutations are possible.

A mathematical representation of processing performed by the OFDMtransmitter can express each block of FIGS. 8 and 9 as a matrix. Theparticular transform is selected to enable the OFDM transmitter totransmit the sequence of samples as ODFM or transformed OFDM on a peruser basis.

If the entire content is to be transmitted using OFDM, then thetransform function T is selected to be the identity matrix shown below,in which elements along a primary negative sloping diagonal are eachequal to one and all other elements in the matrix equal zero.

$T = \begin{bmatrix}1 & 0 & \ldots & 0 & 0 \\0 & 1 & \ldots & 0 & 0 \\\vdots & \vdots & \ddots & \vdots & \vdots \\0 & 0 & \ldots & 1 & 0 \\0 & 0 & \ldots & 0 & 1\end{bmatrix}$

Using the identity matrix as the transform function results in an outputfrom the OFDM transmitter being that of a conventional OFDM signal.Using the identity matrix is substantially the same as if no transformwere performed in the OFDM transmitter.

For the FIG. 8 example, the user of the identity matrix for thetransform T 620 results in the single coded and modulated output beingtransmitted using the entire set of OFDM sub-carriers or an assignedsub-set thereof, be that a sub-band set of sub-carriers or a diversityset of sub-carriers. For the FIG. 9 example, this results in the twocoded and modulated outputs sharing a set of OFDM sub-carriers on twoantennas.

In the opposite extreme, the transform function can be selected to be afast Fourier transform (FFT) performed on the entire sequence of inputsymbols. When the FFT has an equal number of samples used by the IFFTfunctions following the transform, the OFDM transmitter output is asingle carrier conventional FDM transmission. In the particular casewhere the number of samples in the FFT and that used by the IFFTfunctions is the same the FFT and the IFFT are opposite transforms. Theresult of performing the two transforms is substantially the same as ifneither of the two transforms were performed on the sequence of samples.

For the FIG. 8 example, the user of a full sized FFT for the transform T620 results in the single coded and modulated output being transmittedas if it were a single carrier transmission. FIG. 9 differs from FIG. 8in that the output is a MIMO transmission.

For single user implementations, the mode change can be based onfeedback from the receiver, or be made autonomously at the transmitter.In some embodiments, the mode is adaptively changed and/or the transformfunction is selected as a function of one or more of:

SNR—this is really a function of the distance between the receiver andthe transmitter;traffic type—e.g. control channel may need a better channel/performance;head room at the power amplifier in the transmitter as discussedpreviously.

Referring now to FIG. 10, shown is an example frame 800 structure inwhich during a given OFDM symbol duration, only one of the multiplexingstructures are employed, but within a frame consisting of a set of suchOFDM durations multiple multiplexing structures are employed. The framestructure has a two dimensional appearance which is represented ascollection of adjacent columns 810,820. The vertical directionrepresents a transmission band in the frequency domain and thehorizontal direction represents time slots in the time domain. In theexample of FIG. 10, the frame 800 is divided into OFDM time slots 810that are used for OFDM, and time slots 820 that are used for T-OFDM. Asimilar frame (not shown) could be implemented to divide the frame intoOFDM time slots and slots containing direct multiple sub-carriermultiplexing and/or slots containing conventional FDM signals.

The size of the transmission band, the duration of the time slots andthe number of time slots in the frame are all implementation specificparameters. The assignment of the time slots to the various constituentmultiplexing types is also implementation specific, can take any desiredarrangement. In some embodiments, the arrangement of time slots can varyfrom frame to frame. In other embodiments consecutive frames maytransmit the same arrangement of time slots. FIG. 10 can be implementedusing some of the transmitter structures described previously such asthe structures of FIGS. 8 and 9.

FIG. 11 shows an example frame 900 used in accordance with someembodiments of the invention. The frame has a two dimensionalorientation similar to FIG. 10 in which time is represented in thehorizontal direction and frequency in the vertical direction. In FIG.11, in each time slot, the transmission band is segmented into logicalclusters or sub-bands 910, 920. In the illustrated example, each clusterconsists of contiguous sub-carriers. The clusters are shown to be of twodifferent types, that is OFDM clusters 910 and T-OFDM clusters 920. Insome embodiments, the clusters include one or more logical sub-channels,where each sub-channel is a designated grouping of active sub-carriers.An OFDM cluster is a grouping of sub-carriers that each provide anarrowband frequency component of a transmitted signal in a particulartime slot. A T-OFDM cluster is a grouping of sub-carriers thatcollectively provide a wideband frequency sub-band representation of atransmitted signal in a particular time slot.

There are shown to be four clusters in each time slot of the example ofFIG. 11, but the number of clusters in the transmission band and thenumber of active sub-carriers in each cluster are implementationspecific parameters. Furthermore, the size of the transmission band, theduration of the time slots and the number of time slots in the frame areall implementation specific parameters as well. The assignment of theclusters to OFDM and T-OFDM is also implementation specific, where theassignment of OFDM and T-OFDM clusters can take any desired arrangement.In some embodiments, the arrangement of clusters can vary from frame toframe. In other embodiments consecutive frames may transmit the samearrangement of clusters. In the example of FIG. 11, the two dimensionalresource is divided into regions that are used for OFDM, and regionsused for transformed OFDM (TOFDM). A similar frame (not shown) could beimplemented to subdivide the frame into OFDM regions and regionscontaining direct multiple sub-carrier multiplexing and/or regionscontaining conventional FDM signals.

FIG. 11 can be implemented by a multi-carrier OFDM transmitter adaptedto transmit both OFDM and transformed OFDM. Examples of such OFDMtransmitters are shown in FIGS. 8 and 9 and described above.

In FIG. 12, an example frame 1000 is shown for implementing a time andfrequency multiplexing scheme in accordance with some embodiments of theinvention. The frame 1000 is segmented into zones of different size andshape in both time and frequency. Examples of OFDM zones are indicatedby 1010, 1025, 1030, 1045, 1055, 1060 and T-OFDM zones are indicated by1015, 1020, 1035, 1040, 1050, 1065.

The number of zones and manner in which the zones are distributed in theframe are implementation specific parameters. Furthermore, the size ofthe transmission band, the duration of the time slots and the number oftime slots in the frame are all implementation specific parameters aswell. The assignment of zones to OFDM and T-OFDM is also implementationspecific, where the assignment of OFDM and T-OFDM zones can take anydesired arrangement. In some embodiments, the arrangement of zones canvary from frame to frame. In other embodiments consecutive frames maytransmit the same arrangement of zones. In the example of FIG. 12, thetwo dimensional resource is divided into regions that are used for OFDM,and regions used for transformed OFDM (TOFDM). A similar frame (notshown) could be implemented to subdivide the frame into OFDM regions andregions containing direct multiple sub-carrier multiplexing and/orregions containing conventional FDM signals.

FIG. 12 can be implemented by a multi-carrier OFDM transmitter adaptedto transmit both OFDM and T-OFDM. Examples of such OFDM transmitters areshown in FIGS. 8 and 9 and described above.

FIG. 13 shows an example pattern of a pilot design that can be used withsome embodiments of the invention. In FIG. 13, time is shown in thevertical direction and frequency is shown in the horizontal direction.Each circle in the pattern represents content of a particularsub-carrier transmitted at a particular time. A horizontal row of suchcircles represents the sub-carriers transmitted in one or more symbolsin a particular time slot. A vertical column represents the contentstransmitted on a given scheduled sub-carrier over time. There are afinite number of sub-carriers in the frequency direction. It is to beunderstood that the number of sub-carriers in a symbol is a designparameter and that FIG. 11 is to be considered to give only one exampleof a particular size of a symbol.

In FIG. 13 pilots are generally indicated by 1110. Each sub-carrier in afirst time slot transmits a pilot and each sub-carrier in a sixthscheduled time slot transmits a pilot. Data, generally indicated by1120, is transmitted on each subcarrier of second to fifth time slots.The data portion of the frame is transmitted using any of the mechanismsdescribed above, so as to allow both OFDM and T-OFDM, to coexist. Aparticular pilot pattern has been shown in which every first time slotand every fifth time slot thereafter is used for pilots. More generally,many different approaches to inserting pilots can be employed that mayinsert the pilots in the middle of frames, the end of frames, or in ascattered manner to name a few specific examples.

In some implementations pilots are inserted in the frequency domain inparticular sequences to modulate pilot subcarriers to reduce PAPR.Pilots and data may be transmitted by different OFDM symbols. In someimplementations, distributed pilots are used for T-OFDM such that thesame frequency indexes are used for pilots and data for each sequence ofsamples from different users transmitting in the transmission band. Insome implementations sub-band based pilots are used for T-OFDM such thatsame frequency indexes are used for pilots and data for each usertransmitting in the transmission band.

In some embodiments, a pilot is implemented as a time domain trainingsequence. This can be transmitted during a reference symbol at thebeginning, middle or end of frame for example. The reference symbols caninclude a training sequence from a single receiver or training sequencesfrom multiple receivers. In some implementations, the training sequenceis selected to be a sequence with a low PAPR.

Reference to FIG. 14 will now be made in describing an arrangement foran OFDM transmitter 1200 in accordance with an embodiment of theinvention. A sequence of symbols for each of a plurality of users isapplied to a respective processing block to calculate a FFT for thatsequence of symbols, the FFTs being specific examples of transformfunctions. Symbols 1210 for a first user (not shown) are provided to afirst FFT processing block 1212, symbols 1220 for a second user (notshown) are provided to a second FFT processing block 1222 and symbols1230 for a third user (not shown) are provided to a third FFT processingblock 1232. Outputs of each of the three processing blocks 1212, 1222,1232 are provided to a mapping function 1250. An output of the mappingfunction 1250 is provided to an N sample size IFFT processing block1260. An output of the IFFT processing block 1260 is provided to block1270 in which a cyclic prefix is incorporated into the output of theIFFT processing block 1260.

The FFT processing blocks 1212, 1222, 1232 are shown to have FFT samplesizes of M1, M2 and MN, respectively. In some embodiments the samplesizes are the same (M1=M2=MN) in all three FFT processing blocks 1212,1222, 1232. In some embodiments the sample sizes are different for thethree FFT processing blocks 1212, 1222, 1232. Equivalently, the threeFFT processing blocks 1212, 1222, 1232 could be implemented as a singlelarge matrix containing three sub-matrices.

Only three FFT processing blocks 1212, 1222, 1232 are shown in theexample of FIG. 14. However, it is to be understood that the number ofFFT processing blocks is an implementation specific parameter.

In operation, each FFT processing block 1212, 1222, 1232 performs therespective sample size FFT on the sequence of symbols with which it isprovided. The mapping function 1250 applies a mapping to the FFTprocessed sequence of symbols of each user depending on whether sub-bandtransformed OFDM or diversity transformed OFDM is being employed. Fordiversity transformed OFDM, the mapping function 1250 distributes theFFT processed sequence of symbols for each sequence to sub-carriersacross the transmission band, such that two sequences are not mapped tothe same sub-carrier. For sub-band transformed OFDM, the mappingfunction 1250 maps the FFT processed sequence of symbols for eachsequence within a grouping of contiguous sub-carriers in transmissionband, such that two sequences are not mapped to the same grouping ofsub-carriers. The output of the mapping function 1250 is provided to theN sample size IFFT processing block 1260 and the IFFT transforms afrequency spectrum of the transmission band into a time sequence ofsymbols. The block 1270 incorporates the cyclic prefix into the timesequence of symbols prior to transmission.

In some embodiments, a sum of the multiple M sample size FFT outputs ofthe FFT processing blocks 1212, 1222, 1232 equals a number of samples N,which is the same as the number of samples in the N sample size IFFT. Inother embodiments the sum of the multiple M sample size FFT outputs ofthe FFT processing blocks 1212, 1222, 1232 does not equal the number ofsamples N. In some embodiments the number of samples is expanded orpadded to equal N samples before being applied to the N sample size IFFTprocessing block 1260.

In some implementations the OFDM transmitter includes additionalprocessing elements between the FFT processing blocks 1212, 1222, 1232and the IFFT processing block 1260. An example of an additionalprocessing element is a sample size expander to match the number ofsamples of the FFT processing blocks 1212, 1222, 1232 to the number ofsamples of the N sample size IFFT processing block 1260. Another exampleof an additional processing element is a pulse shaping element tofurther reduce the PAPR of the transmission.

In some embodiments of the invention access air interface selection maybe based on the PA (power amplifier) backoff room.

FIGS. 15 to 19 provide context for the above embodiments. Shown arespecific examples of known implementations for OFDM transmitters. Manyof the features shown in these figures may be included in systems thatimplement one or more of the constituent multiplexing structuresdescribed above.

For the purposes of providing context for embodiments of the inventionfor use in a communication system, FIG. 15 shows a base stationcontroller (BSC) 10 which controls wireless communications withinmultiple cells 12, which cells are served by corresponding base stations(BS) 14. In general, each base station 14 facilitates communicationsusing OFDM with mobile and/or wireless terminals 16, which are withinthe cell 12 associated with the corresponding base station 14. Themovement of the mobile terminals 16 in relation to the base stations 14results in significant fluctuation in channel conditions. Asillustrated, the base stations 14 and mobile terminals 16 may includemultiple antennas to provide spatial diversity for communications.

A high level overview of the mobile terminals 16 and base stations 14upon which aspects of the present invention may be implemented. Withreference to FIG. 16, a base station 14 is illustrated. The base station14 generally includes a control system 20, a baseband processor 22,transmit circuitry 24, receive circuitry 26, multiple antennas 28, and anetwork interface 30. The receive circuitry 26 receives radio frequencysignals bearing information from one or more remote transmittersprovided by mobile terminals 16 (illustrated in FIG. 15). A low noiseamplifier and a filter (not shown) may cooperate to amplify and removebroadband interference from the signal for processing. Downconversionand digitization circuitry (not shown) will then downconvert thefiltered, received signal to an intermediate or baseband frequencysignal, which is then digitized into one or more digital streams.

The baseband processor 22 processes the digitized received signal toextract the information or data symbols conveyed in the received signal.This processing may comprise demodulation, decoding, and errorcorrection operations. As such, the baseband processor 22 is generallyimplemented in one or more digital signal processors (DSPs) orapplication-specific integrated circuits (ASICs). The receivedinformation is then sent across a wireless network via the networkinterface 30 or transmitted to another mobile terminal 16 serviced bythe base station 14.

On the transmit side, the baseband processor 22 receives digitized data,which may represent voice, data, or control information, from thenetwork interface 30 under the control of control system 20, and encodesthe data for transmission. The encoded data is output to the transmitcircuitry 24, where it is modulated by a carrier signal having a desiredtransmit frequency or frequencies. A power amplifier (not shown) willamplify the modulated carrier signal to a level appropriate fortransmission, and deliver the modulated carrier signal to the antennas28 through a matching network (not shown). Various modulation andprocessing techniques available to those skilled in the art are used forsignal transmission between the base station and the mobile terminal.

With reference to FIG. 17, a mobile terminal 16 configured according toone embodiment of the present invention is illustrated. Similarly to thebase station 14, the mobile terminal 16 will include a control system32, a baseband processor 34, transmit circuitry 36, receive circuitry38, multiple antennas 40, and user interface circuitry 42. The receivecircuitry 38 receives radio frequency signals bearing information fromone or more base stations 14. A low noise amplifier and a filter (notshown) may cooperate to amplify and remove broadband interference fromthe signal for processing. Downconversion and digitization circuitry(not shown) will then downconvert the filtered, received signal to anintermediate or baseband frequency signal, which is then digitized intoone or more digital streams.

The baseband processor 34 processes the digitized received signal toextract the information or data symbols conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations. The baseband processor 34 is generallyimplemented in one or more digital signal processors (DSPs) andapplication specific integrated circuits (ASICs).

For transmission, the baseband processor 34 receives digitized data,which may represent voice, data, or control information, from thecontrol system 32, which it encodes for transmission. The encoded datais output to the transmit circuitry 36, where it is used by a modulatorto modulate a carrier signal that is at a desired transmit frequency orfrequencies. A power amplifier (not shown) will amplify the modulatedcarrier signal to a level appropriate for transmission, and deliver themodulated carrier signal to the antennas 40 through a matching network(not shown). Various modulation and processing techniques available tothose skilled in the art are used for signal transmission between themobile terminal and the base station.

In operation, OFDM may be used for the uplink and or the downlinktransmission between the base stations 14 to the mobile terminals 16.Each base station 14 is equipped with “n”>=1 transmit antennas 28, andeach mobile terminal 16 is equipped with “m”>=1 receive antennas 40.Notably, the respective antennas can be used for reception andtransmission using appropriate duplexers or switches and are so labeledonly for clarity.

With reference to FIG. 18, a logical OFDM transmission architecture willbe described. Initially, the base station controller 10 will send datato be transmitted to various mobile terminals 16 to the base station 14.The base station 14 may use the channel quality indicators (CQIs)associated with the mobile terminals to schedule the data fortransmission as well as select appropriate coding and modulation fortransmitting the scheduled data. The CQIs may be directly from themobile terminals 16 or determined at the base station 14 based oninformation provided by the mobile terminals 16. In either case, the CQIfor each mobile terminal 16 is a function of the degree to which thechannel amplitude (or response) varies across the OFDM frequency band.

Scheduled data 44, which is a stream of symbols, is scrambled in amanner reducing the peak-to-average power ratio associated with the datausing data scrambling logic 46. A cyclic redundancy check (CRC) for thescrambled data is determined and appended to the scrambled data usingCRC adding logic 48. Next, channel coding is performed using channelencoder logic 50 to effectively add redundancy to the data to facilitaterecovery and error correction at the mobile terminal 16. Again, thechannel coding for a particular mobile terminal 16 is based on the CQI.In some implementations, the channel encoder logic 50 uses known Turboencoding techniques. The encoded data is then processed by rate matchinglogic 52 to compensate for the data expansion associated with encoding.

Bit interleaver logic 54 systematically reorders the bits in the encodeddata to minimize the loss of consecutive data bits. The resultant databits are systematically mapped into corresponding symbols depending onthe chosen baseband modulation by mapping logic 56. In some embodiments,Quadrature Amplitude Modulation (QAM) or Quadrature Phase Shift Key(QPSK) modulation is used. The degree of modulation may be chosen basedon the CQI for the particular mobile terminal. The symbols may besystematically reordered to further bolster the immunity of thetransmitted signal to periodic data loss caused by frequency selectivefading using symbol interleaver logic 58.

At this point, groups of bits have been mapped into symbols representinglocations in an amplitude and phase constellation. When spatialdiversity is desired, blocks of symbols are then processed by space-timeblock code (STC) encoder logic 60, which modifies the symbols in afashion making the transmitted signals more resistant to interferenceand more readily decoded at a mobile terminal 16. The STC encoder logic60 will process the incoming symbols and provide “n” outputscorresponding to the number of transmit antennas 28 for the base station14. The control system 20 and/or baseband processor 22 as describedabove with respect to FIG. 2 will provide a mapping control signal tocontrol STC encoding. At this point, assume the symbols for the “n”outputs are representative of the data to be transmitted and capable ofbeing recovered by the mobile terminal 16.

For the present example, assume the base station 14 has two antennas 28(n=2) and the STC encoder logic 60 provides two output streams ofsymbols. Accordingly, each of the symbol streams output by the STCencoder logic 60 is sent to a corresponding IFFT function 62,illustrated separately for ease of understanding. Those skilled in theart will recognize that one or more processors may be used to providesuch digital signal processing, alone or in combination with otherprocessing described herein. The IFFT functions 62 will operate on therespective symbols to provide an inverse Fourier Transform. The outputof the IFFT functions 62 provides symbols in the time domain. The timedomain symbols are grouped into frames, which are associated with aprefix by prefix insertion logic 64. Each of the resultant signals isup-converted in the digital domain to an intermediate frequency andconverted to an analog signal via the corresponding digitalup-conversion (DUC) and digital-to-analog (D/A) conversion circuitry 66.The resultant (analog) signals are then simultaneously modulated at thedesired RF frequency, amplified, and transmitted via the RF circuitry 68and antennas 28. Notably, pilot signals known by the intended mobileterminal 16 are scattered among the sub-carriers. The mobile terminal16, which is discussed in detail below, will use the pilot signals forchannel estimation.

Reference is now made to FIG. 19 to illustrate reception of thetransmitted signals by a mobile terminal 16. Upon arrival of thetransmitted signals at each of the antennas 40 of the mobile terminal16, the respective signals are demodulated and amplified bycorresponding RF circuitry 70. For the sake of conciseness and clarity,only one of the two receive paths is described and illustrated indetail. Analog-to-digital (A/D) converter and down-conversion circuitry72 digitizes and downconverts the analog signal for digital processing.The resultant digitized signal may be used by automatic gain controlcircuitry (AGC) 74 to control the gain of the amplifiers in the RFcircuitry 70 based on the received signal level.

Initially, the digitized signal is provided to synchronization logic 76,which includes coarse synchronization logic 78, which buffers severalOFDM symbols and calculates an auto-correlation between the twosuccessive OFDM symbols. A resultant time index corresponding to themaximum of the correlation result determines a fine synchronizationsearch window, which is used by fine synchronization logic 80 todetermine a precise framing starting position based on the headers. Theoutput of the fine synchronization logic 80 facilitates frameacquisition by frame alignment logic 84. Proper framing alignment isimportant so that subsequent FFT processing provides an accurateconversion from the time domain to the frequency domain. The finesynchronization algorithm is based on the correlation between thereceived pilot signals carried by the headers and a local copy of theknown pilot data. Once frame alignment acquisition occurs, the prefix ofthe OFDM symbol is removed with prefix removal logic 86 and resultantsamples are sent to frequency offset correction logic 88, whichcompensates for the system frequency offset caused by the unmatchedlocal oscillators in the transmitter and the receiver. Thesynchronization logic 76 may include frequency offset and clockestimation logic 82, which is based on the headers to help estimate sucheffects on the transmitted signal and provide those estimations to thecorrection logic 88 to properly process OFDM symbols.

At this point, the OFDM symbols in the time domain are ready forconversion to the frequency domain using FFT processing logic 90. Theresults are frequency domain symbols, which are sent to processing logic92. The processing logic 92 extracts the scattered pilot signal usingscattered pilot extraction logic 94, determines a channel estimate basedon the extracted pilot signal using channel estimation logic 96, andprovides channel responses for all sub-carriers using channelreconstruction logic 98. In order to determine a channel response foreach of the subcarriers, the pilot signal is essentially multiple pilotsymbols that are scattered among the data symbols throughout the OFDMsubcarriers in a known pattern in both time and frequency. Examples ofscattering of pilot symbols among available sub-carriers over a giventime and frequency plot in an OFDM environment are found in PCT PatentApplication No. PCT/CA2005/000387 filed Mar. 15, 2005 assigned to thesame assignee of the present application. Continuing with FIG. 19, theprocessing logic compares the received pilot symbols with the pilotsymbols that are expected in certain sub-carriers at certain times todetermine a channel response for the sub-carriers in which pilot symbolswere transmitted. The results are interpolated to estimate a channelresponse for most, if not all, of the remaining sub-carriers for whichpilot symbols were not provided. The actual and interpolated channelresponses are used to estimate an overall channel response, whichincludes the channel responses for most, if not all, of the sub-carriersin the OFDM channel.

The frequency domain symbols and channel reconstruction information,which are derived from the channel responses for each receive path areprovided to an STC decoder 100, which provides STC decoding on bothreceived paths to recover the transmitted symbols. The channelreconstruction information provides equalization information to the STCdecoder 100 sufficient to remove the effects of the transmission channelwhen processing the respective frequency domain symbols.

The recovered symbols are placed back in order using symbolde-interleaver logic 102, which corresponds to the symbol interleaverlogic 58 of the transmitter. The deinterleaved symbols are thendemodulated or de-mapped to a corresponding bitstream using de-mappinglogic 104. The bits are then deinterleaved using bit de-interleaverlogic 106, which corresponds to the bit interleaver logic 54 of thetransmitter architecture. The de-interleaved bits are then processed byrate de-matching logic 108 and presented to channel decoder logic 110 torecover the initially scrambled data and the CRC checksum. Accordingly,CRC logic 112 removes the CRC checksum, checks the scrambled data intraditional fashion, and provides it to the de-scrambling logic 114 forde-scrambling using the known base station de-scrambling code to recoverthe originally transmitted data 116.

In parallel to recovering the data 116, a CQI, or at least informationsufficient to create a CQI at the base station 14, is determined andtransmitted to the base station 14. As noted above, the CQI may be afunction of the carrier-to-interference ratio (CR), as well as thedegree to which the channel response varies across the varioussub-carriers in the OFDM frequency band. The channel gain for eachsub-carrier in the OFDM frequency band being used to transmitinformation is compared relative to one another to determine the degreeto which the channel gain varies across the OFDM frequency band.Although numerous techniques are available to measure the degree ofvariation, one technique is to calculate the standard deviation of thechannel gain for each subcarrier throughout the OFDM frequency bandbeing used to transmit data.

FIGS. 15 to 19 each provide a specific example of a communication systemor elements of a communication system that could be used to implementembodiments of the invention. It is to be understood that embodiments ofthe invention can be implemented with communications systems havingarchitectures that are different than the specific example, but thatoperate in a manner consistent with the implementation of theembodiments as described herein.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

What is claimed is:
 1. An apparatus, comprising: a baseband processorcoupled to transmit circuitry and at least one antenna, wherein thebaseband processor is configured to: transmit signaling to a transmitterfor transform selection; receive, based on the transmitted signaling,one of transformed or non-transformed orthogonal frequency divisionmultiplexing (OFDM) signals, wherein the transformed OFDM uplink signalsinclude a first plurality of symbols that have undergone coding andmodulation, discrete Fourier transform (DFT) transformation, and aninverse Fast Fourier transform (IFFT), wherein the non-transformed OFDMuplink signals include a second plurality of symbols that have undergonecoding and modulation and the IFFT; wherein the second plurality ofsymbols have not undergone the DFT transform; wherein thenon-transformed OFDM uplink signals include a plurality of clusters,wherein a cluster is a set of contiguous subcarriers.
 2. The apparatusof claim 1, wherein the non-transformed OFDM uplink signals support twomodes: a first mode wherein the clusters of non-transformed OFDM uplinksignals are contiguous and a second mode wherein the clusters ofnon-transformed OFDM uplink signals are non-contiguous.
 3. The apparatusof claim 2, wherein the transformed OFDM uplink signals support thefirst mode and the second mode.
 4. The apparatus of claim 1, whereintransformed OFDM signals are selected based at least in part on thefirst plurality of symbols corresponding to an uplink control channel.5. The apparatus of claim 1, wherein the baseband processor is furtherconfigured to: receive a plurality of pilot signals, wherein the pilotsignals are time-division multiplexed with the transformed ornon-transformed OFDM signals.
 6. The apparatus of claim 5, wherein theplurality of pilot signals for each time-division slot are comprisedwithin a plurality of contiguous sub carriers in frequency.
 7. Theapparatus of claim 1, wherein the transformed OFDM uplink signals andthe non-transformed OFDM uplink signals are time-division multiplexed.8. A base station, comprising: at least one antenna; transmit circuitrycoupled to the at least one antenna; and a baseband processor coupled tothe transmit circuitry and the at least one antenna, wherein the basestation is configured to: transmit signaling to a transmitter fortransform selection; receive, based on the transmitted signaling, one oftransformed or non-transformed orthogonal frequency divisionmultiplexing (OFDM) signals, wherein the transformed OFDM uplink signalsinclude a first plurality of symbols that have undergone coding andmodulation, discrete Fourier transform (DFT) transformation, and aninverse Fast Fourier transform (IFFT), wherein the non-transformed OFDMuplink signals include a second plurality of symbols that have undergonecoding and modulation and the IFFT; wherein the second plurality ofsymbols have not undergone the DFT transform; wherein thenon-transformed OFDM uplink signals include a plurality of clusters,wherein a cluster is a set of contiguous subcarriers.
 9. The basestation of claim 8, wherein the non-transformed OFDM uplink signalssupport two modes: a first mode wherein the clusters of non-transformedOFDM uplink signals are contiguous and a second mode wherein theclusters of non-transformed OFDM uplink signals are non-contiguous. 10.The base station of claim 9, wherein the transformed OFDM uplink signalssupport the first mode and the second mode.
 11. The base station ofclaim 8, wherein transformed OFDM signals are selected based at least inpart on the first plurality of symbols corresponding to an uplinkcontrol channel.
 12. The base station of claim 8, wherein the basebandprocessor is further configured to: receive a plurality of pilotsignals, wherein the pilot signals are time-division multiplexed withthe transformed or non-transformed OFDM signals.
 13. The base station ofclaim 12, wherein the plurality of pilot signals for each time-divisionslot are comprised within a plurality of contiguous sub carriers infrequency.
 14. The base station of claim 8, wherein the transformed OFDMuplink signals and the non-transformed OFDM uplink signals aretime-division multiplexed.
 15. A method for operating a base station,the method comprising: transmitting signaling to a transmitter fortransform selection; receiving, based on the transmitted signaling, oneof transformed or non-transformed orthogonal frequency divisionmultiplexing (OFDM) signals, wherein the transformed OFDM uplink signalsinclude a first plurality of symbols that have undergone coding andmodulation, discrete Fourier transform (DFT) transformation, and aninverse Fast Fourier transform (IFFT), wherein the non-transformed OFDMuplink signals include a second plurality of symbols that have undergonecoding and modulation and the IFFT; wherein the second plurality ofsymbols have not undergone the DFT transform; wherein thenon-transformed OFDM uplink signals include a plurality of clusters,wherein a cluster is a set of contiguous subcarriers.
 16. The method ofclaim 15, wherein the non-transformed OFDM uplink signals support twomodes: a first mode wherein the clusters of non-transformed OFDM uplinksignals are contiguous and a second mode wherein the clusters ofnon-transformed OFDM uplink signals are non-contiguous.
 17. The methodof claim 15, wherein transformed OFDM signals are selected based atleast in part on the first plurality of symbols corresponding to anuplink control channel.
 18. The method of claim 15, the method furthercomprising: receiving a plurality of pilot signals, wherein the pilotsignals are time-division multiplexed with the transformed ornon-transformed OFDM signals.
 19. The method of claim 18, wherein theplurality of pilot signals for each time-division slot are comprisedwithin a plurality of contiguous sub carriers in frequency.
 20. Themethod of claim 15, wherein the transformed OFDM uplink signals and thenon-transformed OFDM uplink signals are time-division multiplexed.